Disease of-horticultural-crops-their-management1

Disease of Horticultural Crops & their
Management
ICAR e-Course
For
B.Sc (Agriculture) and B.Tech (Agriculture)

Index
SN Lecture Page No
1. Diseases of Citrus 5-9
2. Diseases of Mango 10-16
3. Diseases of Banana 17-23
4. Diseases of Grapes 24-27
5. Diseases of Pomegranate and Papaya 28-32
6. Diseases of Guava 33-35
7. Diseases of Apple 36-43
8. Diseases of Chilli 44-51
9. Diseases of Brinjal 52-57
10. Diseases of Bhendi 58-61
11. Diseases of Potato 62-72
12. Diseases of Cucurbits 73-88
13. Diseases of Crucifers 89-109
14. Diseases of Tomato 110-120
15. Diseases of Beans 121-127
16. Diseases of Onion & Garlic 128-137

17. Diseases of Coconut and Oil palm 138-145
18. Diseases of Mulberry 146-148
19. Diseases of Betelvine 149-152
20. Diseases of Coffee 153-156
21. Diseases of Tea 157-159
22. Diseases of Rose 160-164
23. Diseases of Chrysanthemum 165-167
24. Diseases of Jasmine and Crossandra 168-169
25. Diseases of Crossandra 170-171

Lecture 01 - Diseases of Citrus
Gummosis: Phytophthora parasitica, P. palmivora,P. citrophthora
Symptoms
The symptoms appear as yellowing of leaves, followed by cracking of bark and profuse
gumming on the surface. The main source of infection is infected planting material. As a result
of severe gumming, the bark becomes completely rotten and the tree dries owing to girdling
effect. Prior to death, the plant usually blossoms heavily and dies before the fruits mature. In
such cases, the disease is called foot rot or collar-rot.
Pathogen
Aseptate, intercellular & intracellular hypha. Sporangia are ovoid or ellipsoid.
Sporangium attached with the sporangium at the right angles sporangia germinate to release
zoospore.
Favourable conditions
Prolonged contact of trunk with water as in flood irrigation; water logged areas and heavy
soils.
Mode of spread and survival
Soil inhabitants, Sporangia spread by splashing rain water, irrigation water and wind.
Management
Preventive measures like selection of proper site with adequate drainage, use of resistant
rootstocks and avoiding contact of water with the tree trunk by adopting ring method of
irrigation are effective. Alternatively the disease portions are scraped-out with a sharp knife and
the cut surface is disinfected with Mercuric chloride (0.1%) or Potassium permanganate solution
(1%) using a swab of cotton. Painting 1 m of the stem above the ground level with Bordeaux
helps in controlling the disease. Also spraying and drenching with Ridomil MZ 72@ 2.75 g/l or
Aliette (2.5 g/l) is effective in controlling the disease.
Scab/Verucosis : Elsinoe fawcetti
Symptoms
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The lesions in early stages appear on the underside of the leaves as small semi-translucent
dots, which finally become sharply defined pustular elevations. In later stages, leaves often
become distorted, wrinkled, stunted and deformed. On the fruit, lesions consist of corky
projections, which often break into scabs. The opposite surface corresponding to the warty
growth shows a circular depression with a pink to red center.
Pathogen
Ascostroma are simple, innate, intra or sub epidermal, partially erumpent at maturity,
small pulvinate to crustose. Asci are ovoid. Ascospares are 1-3 septate oblong to elliptical and
hyaline to yellowing conidia are produced in acervuli. Conidia are hyaline, ablong, elliptical
with two minute droplets of their ends.
Mode of Spread and Survival
The pathogen survive in off season as ascospores and spreads through Conidia.
Management
The diseased leaves, twigs and fruits should be collected and destroyed. Spraying of
Carbendazim 0.1% is quite effective
Canker : Xanthomonas campestris pv citri
Symptoms
Acid lime, lemon and grapefruit are
affected. Rare on sweet oranges and mandarins.
Affects leaf, twig and fruits. In canker, leaves are not
distorted.Lesions are typically circular with yellow
halo; appear on both sides of leaf, severe in acid lime
(difference from scab) When lesions are produced on
twigs, they are girdled and die. On fruits, canker
lesions reduce market value.
Pathogen
It is Gram negative, non spore forming, aerobic bacteria. It is rod shaped, forms chains
and capsules and is motile by one polar flagellum.
Free moisture for 20 minutes, 20-30°C.
Mode of survival and spread
Wind and rain splashes. Survives in infected leaves for 6 months. Injury caused by leaf miner
helps the entry of the bacterium.
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Disease Cycle
Management
Streptomycin sulphate 500-1000 ppm; or Phytomycin 2500 ppm or Copper oxychloride
0.2% at fortnight intervals. Control leaf miner when young flush is produced. Prune badly
infected twigs before the onset of monsoon.
Tristeza or quick decline : Citrus tristeza virus (CTV)
Symptoms
Lime is susceptible both as seedling or buddling on any
root stock. But mandarin and sweet orange seedlings or on
rough lemon, trifoliate orange, citrange; Rangpur lime root
stocks tolerant; susceptible root stocks are grapefruit and sour
orange.
In sweet orange or mandarin on susceptible root stocks,
leaves develop deficiency symptoms and absise. Roots
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decay, twigs die back. Fruit set diminishes; only skeleton remains. Fine pitting of inner face of
bark of sour orange stock. Grapefruit and acid lime are susceptible irrespective of root stock. Acid lime leaves
show large number of vein flecks (elongated translucent area). Tree stunted and dies yield very much reduced. Fruits
are small in size. Use of infected bud wood and Toxoptera citricida (aphid) is the important vector.
Pathogen
Citrus tristeza virus is long, flexuous rod and measure 2000x 12nm in size. Three strains
viz., mild, severe and seedling yellow are reported.
Mode of spread
Use of infected bud wood Toxoptera citricida (aphid) is the important vector.
Management
For sweet orange and mandarin, avoid susceptible root stocks. For acid lime, use seedling
preimmunised with mild strain of tristeza.
Exocortis of scaly butt: Viroid
Symptoms
Affects only Rangpur lime, trifoliate orange and citrange root stocks. Vertical cracking
and scaling of bark in the entire, root stock. Extreme stunting of plant.
Pathogen
Viroid is free RTVA without protein coat.
Transmission normally occurs through infected bud, wood, and contaminated tools. Not
through vector and seed.
Management
Spray with any one of the systemic insecticide to control the aphid vector. Use virus-free
certified bud wood; use tolerant stocks like rough lemon Periodically wash budding knife with
disodium Phosphate solution.
Greening: Liberobactor asiaticum (Phloem limited bacteria)
Symptoms
This disease affects almost all citrus varieties irrespective of root stock. Stunting of leaf,
sparse foliation, twig die back, poor crop of predominantly greened, worthless fruits. Sometimes
only a portion of tree is affected.A diversity of foliar chlorosis. A type of mottling resembling
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zinc deficiency often predominates. Young leaves appear normal but soon assume on outright
position, become leathery and develop prominant veins and dull olive green colour.
Green circular dots on leaves. Many twigs become upright and produce smaller leaves. Fruits small,
lopsided with curved columella. The side exposed to direct sunlight develops full orange colour
but the other side remain dull olive green. Low in juice and soluble solids, high in acid.
Worthless either as fresh fruit or for processing. Seeds poorly developed, dark coloured, aborted.
Pathogen
Rickettsia like organisam
Mode of spread
Infected budwood; psyllid vector-Diaphorina citri
Management
Control psyllids with insecticides. Use pathogen free bud wood for propagation. 500 ppm
tetracycline spray, requires fortnightly application.
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Lecture 02 - Diseases of Mango (2 Lectures)
Anthracnose: Colletotrichum gloeosporioides
Symptoms:
The disease appears on young leaves, stem, inflorescence and fruits. Leaves show oval or
irregular, greyish-brown spots which may coalesce to cover larger area of the leaf. The affected
leaf tissues dry and shred. Leaves on infected petioles droop and fall. On young stem, grey-
brown spots develop. These enlarge and cause girdling and drying of the affected area. The
disease appears on young leaves, stem, inflorescence and fruits.
Often, black necrotic areas develop on the twigs from the tip downwards causing a
dieback. In humid weather, minute, black dots develop on the floral organs. The infected flower-
parts ultimately shed resulting in partial or complete deblossoming. Latent infections of fruit are
established before harvest. The ripening fruits show typical anthracnose. Black spots appearing
on skin of the affected fruits gradually become sunken and coalesce.
Pathogen
Mycelium septate and coloured. Conidia Single celled, hyaline, small and elongated.
On dried leaves, defoliated branches mummified flowers and flower brackets. Contact with
diseased fruit during transport and storage. The secondary spread is through airborne conidia.
Temperature of 25°C and Relative Humidity 95-97%
Disease cycle
The survival of pathogen in detached diseased twigs and leaves lying on surface of soil
and in diseased twigs attached to the tree. They successfully reproduced the disease by
inoculating leaves, petioles, stems and fruits. The optimum temperature for infection was found
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to be 25˚C. The disease spreads rapidly in the rainy season. Cloudy and misty weather during
flowering favors damage to the infected floral parts.
The pathogen causes severe leaf spotting. The appearance of spots in more concentration
at the stem-end and sometimes in stripes down the sides of the fruits suggested distribution of
spores by rain water over surface of the fruit. The fungus can enter the pores of green fruits. The
latent infection of mature fruits may take place through lenticels. The fungus apparently infects
the fruit while it is green and develops in flesh during ripening.
Management
Spray P. fluorescens (FP 7) at 3 weeks interval commencing from October at 5g/like on flower branches.
5-7 sprays one to be given on flowers and bunches. Before storage, treat with hot water, (50-55°C) for 15 minutes or
dip in Benomyl solution (500ppm) or Thiobendazole (1000ppm) for 5 minutes
Powdery mildew: Oidium mangiferae (Acrosporum mangiferae)
Symptoms
Powdery mildew is one of the most serious diseases of mango affecting almost all the varieties.
The characteristic symptom of the disease is the white superficial powdery fungal growth on
leaves, stalk of panicles, flowers and young fruits. The affected flowers and fruits drop pre-
maturely reducing the crop load considerably or might even prevent the fruit set. Rains or mists
accompanied by cooler nights during flowering are congenial for the disease spread.
Pathogen
Mycelium is ectophytic. Conidiophores short, hyaline and conidia single celled -barrel
shaped, produced in chain. Fungus is odium type.
Survives as dormant mycelium in affected leaves. Secondary spread by air borne
conidia.
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Disease Cycle
Spores blown wind from infected areas readily adhere to hairy, unopened flowers near tip
of the inflorescence and germinate in five to seven hours. Fungus grows rapidly during cloudy
weather accompanied with heavy morning mist. Warm, humid weather and low night
temperatures favour dissemination of the pathogen. Overall disease development is favoured by
high humidity.
Management
Dusting the plants with fine sulphur (250-300 mesh) at the rate of 0.5 kg/tree. The first
application may be soon after flowering, second 15 days later (or) spray with Wettable sulphur
(0.2%), (or) Carbendazim (0.1%),(or) Tridemorph ( 0.1%),(or) Karathane (0.1%).
Mango malformation : Fusarium moliliforme var. subglutinans
Symptoms
Three types of symptoms: bunchy top
phase, floral malformation and vegetative
malformation. In bunchy top phase in nursery
bunching of thickened small shoots, bearing
small rudimentally leaves. Shoots remain short and
stunted giving a bunchy top appearance. In
vegetative malformation, excessive vegetative
branches of limited growth in seedlings. They are swollen with short internodes forming
bunches of various size and the top of the seedlings shows bunchy top appearance. In
malformation of inflorescens, shows variation in the panicle. Malformed head dries up in black
mass and persist for long time. Secondary branches are transformed into number of small leaves
giving a witches broome appearance.
Pathogen
Micro conidia are one or 2 celled, oval to fusiform and produced from polyphialides.
Macro conidia are rarely produced. They are 2 -3 celled and falcate. Chlamydospores are not
produced.
Mode of spread
Diseased propagatives materials.
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Disease Cycle
Management
Diseased plants should be destroyed .Use of disease free planting material. Incidence
reduced by spraying 100-200ppm NAA during October. Pruning of diseased parts along the
basal 15-20 cm apparently healthy portions. This is followed by the spraying of Carbendazim
(0.1%) or Captafol (0.2%).
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Stem end rot: Diplodia natalensis
Symptoms
The dark epicarp around the base of the pedicel. In the initial stage the affected area
enlarges to form a circular, black patch. Under humid atmosphere extends rapidly and turns the
whole fruit completely black within two or three days. The pulp becomes brown and somewhat
softer. Dead twigs and bark of the trees, spread by rains
Pathogen
The fungus produces brown to black, globose to sub globose, pyriform, erumpent
pycnidia that are ostiolate. They are 120-155x370-465 micron meter. Two types of conidia are
produced within a pycnidium. One is hyaline, thin walled and unicellular.Tha another one is
thick walled and bicelled with four to six longitudinal striations.
The fungus persists in infected plant parts which serve as source of inoculum.
Management
Prune and destroy infected twigs and spray Carbendazim or Thiophanate Methyl(0.1%) or Chlorathalonil
(0.2%) as fortnightly interval during rainy season.
Red-rust: Cephaleuros virescens
Symptoms
Algae attacks foliage and young twigs. Rusty spots appear on leaves, initially as circular,
slightly elevated, coalesce to form irregular spots. The spores mature fall off and leave cream to
white valvet texture on the surface of the leaves.
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Pathogen
Cephaleuros virescens after a period of vegetative growth develops its reproductive
structures.Sporangia formed directly on the thallus are sessile and thick walled with orange
pigments. hey are formed singly on the vegetative filaments. When the sporangia are riped the
con tents are converted into Zoospores and liberated through an opening in the wall. The
Zoospores are orange in colour, ovoid and swim actively by means of cilia.
Management
Bordeaux mixture (0.6%) or Copper oxychloride 0.25%
Grey Blight : Pestalotia mangiferae
Symptoms
Brown spots develop on the margin and at the tip of the leaf lamina. They increase in
size and become dark brown. Black dots appear on the spots which are acervuli of the fungus.
Survive on mango leaves for over a year. Spreads through wind borne conidia. Heavy infection
is noticed during the monsoon when the temperature is 20-25˚C and high humidity.
Pathogen
Acervuli seen as minute black dots on affected portion. Mycelium is colored and septate.
Conidia five celled middle three cells are colored and the end cells are hyaline Slender 3-5
appendages are produced at the apex of the spore.
Survive on mango leaves for over a year. Spreads through wind borne conidia.
Heavy infection is noticed during the monsoon when the temperature is 20-25˚C and high
humidity.
Management
Remove and destroy infected plant parts. Spraying copper oxychloride 0.25 Mancozeb 0.25%
or Bordeaux mixture 1.0%.
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Sooty mould : Capnodium mangiferae
Symptoms
The fungi produce mycelium which is superficial and dark. They row on sugary
secretions of the plant hoppers. Black encrustation is formed which affect the photosynthetic
activity. The fungus grows on the leaf surface on the sugary substances secreted by jassids,
aphids and scale insects.
The fungus grows on the leaf surface on the sugary substances secreted by Jassids,Aphids
and scale insects.
Management
Management should be done for insects and sooty moulds simultaneously. Controlling of
insect by spraying systemic insecticides like Monocrotophos or methyl dematon .After that spray
starch solution (1kg Starch/Maida in 5 litres of water. Boiled and dilute to 20 liters) .Starch dries
and forms flake which are removed along with the fungus.
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Lecture 03 - Diseases of Banana (2 Lectures)
Panama disease :Fusarium oxysporum f. spcubense
Economic Importance
The first major disease which attacked banana was called Panama disease from the area
where it first became serious. Banana wilt is a soil-borne fungal disease and gets entry in the
plant body through roots and wounds caused by nematodes. It is most serious in poorly drained
soil. Disease spreads through infected suckers.
Symptoms
Yellowing of the lower most leaves starting from margin to midrib of the leaves.
Yellowing extends upwards and finally heart leaf alone remains green for some time and it is
also affected. The leaves break near the base and hang down around pseudostem. Longitudinal
splitting of pseudostem. Discolouration of vascular vessels as red or brown streaks. The fungus
spreads through use of infected rhizomes Continuous cultivation results in build up of inoculum.
Pathogen
Mycelium is septate, hyaline and branched. Fungus produces micro, macro conidia and
also chlamydospores. Micro conidia - Single celled or rarely one septate hyaline elliptical or
oval. Macro conidia - Sickle shaped hyaline, 3-5 septate and tapering at both ends.
Chalamydospores - Thick walled, spherical to oval, hyaline to slightly yellowish in colour.
The pathogen is soil borne. It survives in soil as chlamydospores for longer periods. The
primary spread of the disease is through infected rhizomes and secondary spread is through
irrigation water. Continuous cultivation results in build up of inoculum.
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Management
Avoid growing of susceptible cultivars viz., Rasthali, Monthan, Red banana and
Virupakshi. Grow resistant cultivar Poovan. Since nematode predispose the disease pairing and
prolinage wit Carbofuran granules. Corm injection of 3 ml of 2% Carbendezim injected in the
corm by making a hole to a depth of 10cm with 45 0 angle on 5 th and 7 th month as
mentioned earlier.
Moko disease : Pseudomonas solanacearum / Burkholderia solanacearum
Symptoms
Leaves become yellow and progress upwards. The petiole breaks and leaves hang. When it
is cut open discolouration in vascular region with pale yellow to dark brown colour. The
discolouration is in the central portion of the corm. Internal rot of fruits with dark brown
discoloration. When the pseudostem is cut transversely bacterial ooze can be seen.
Pathogen
It is rod shaped, gram negative bacterium with one polar flagellum.
The pathogen is soil borne, it survives in susceptible hosts like banana and Heliconia spp.
Management
Eradicate infected plant. Expose soil to direct sunlight. Use of clean planting material.
Fallowing and crop rotation is advisable.Disinfection of pruning of tools. Providing good
drainage.
Tip over or Heart rot: Erwinia carotovora subsp. carotovora
Symptoms
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The base of the pseudostem and upper portion of the corm are affected and leads to
rotting. Young 1-3 month old plantation susceptible during summer months.
Management
Plant disease free suckers. Remove infected plants and destroy. Drench with Methoxy
ethyl mercuric chloride (Emisan-6) 0.1 / or Sodium hypohlorite 10% or Bleaching powder 20g
/litre/tree.
Sigatoka disease : Mycosphaerella musicola (Cercospora musae)
Symptoms
On leaves small light yellow or brownish green narrow streaks appear. They enlarge in
size becomes linear, oblong, brown to black spots with dark brown brand and yellow halo.
Black specks of fungal fruitification appear in the affected leaves. Rapid drying and defoliation
of the leaves.
Pathogen
Conidia are elongated, narrow and multi septate and measure 20 – 80 x 2-6micron meter.
Perithecia are dark brown to black and asci are oblong, clavate and measure 28.8- 36.8x8.0-10.8
micron meter. Ascospores are one septate, hyaline, obtuse with upper cell slightly broader.
Disease Cycle
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Management
Removal and destruction of the affected leaves. Spray Propiconazole + Carbendazim
0.1% or Chlorothalonil 0.25%. Add wetting agent such as teepol or sandovit added at the rate of
1ml/lit of water.
Cigar end Rot (Verticillium theobromae, Trachsphaera fructigena and Gloeosporium musarum)
Symptoms
A black necrosis spread from the perianth into the tip of immature fingers. The rotted
portion of the banana finger is dry and tends to adhere to fruits (appears similar to the ash of a
cigar).
Pathogen
Conidiophores are usually solitary or in small groups. Conidia are hyaline, oblong to
cylindrical. They are borne at the end of tapering phialides, aggregated into rounded,
mucilaginous translucent heads.
Control:
Removal of pistil and perianth by hand 8-10 days after bunch formation and spraying the
bunch with Dithane M -45 (0.1%) or Topsin M (0.1%) controls the disease effectively.
Minimising bruising; prompt cooling to 14°C; proper sanitation of handling facilities reduce the
incidence in the cold storage.
Anthracnose: Gloeosporium gloeosporioides
Symptoms:
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The skin at the distal ends of the fingers turn black shrivels. The fungus produces masses
of conidia which form a pinkish coat. The entire fruit and bunch is affected in severe cases.
Sometimes main stalk of bunch diseased. The bunch becomes black and rotten. Acervuli
produces cylindrical conidiophores, hyaline, septate, branched. Conidia hyaline, non-septate,
oval to elliptical.
Pathogen
Acervuli are usually rounded or sometimes elongated, erumpent. Conidiophores are
cylindrical, tapered towards the apex, hyaline and septate. Conidia are hyaline, aseptate, oval to
ellipitical in shape.
The spread of the disease is by air borne conidia and numerous insects which frequently
visit banana flowers also spread the disease.
Management
Post harvest dipping of fruits in Carbendazim 400 ppm, or Benomyl 1000 ppm, or
Aureofunginsol 100 ppm.
Freckle or Black Spot: Phyllostictina musarum
Symptoms
Minute raised dark brown spots appear with black dots in the centre on leaves and fruits.
On the fruits the pathogen is confined to the skin. The fungus produces pycnidium which are
dark. conidiophores simple, short, elongate. Conidia are byline, single celled ovoid. Fungus
survives in infected plant debris. Conidia spread by rain water and wind.
Pathogen
The fungus produces pycnidia and pycnidiospores. Pycnidiospores are needle shape,
hyaline and multi septate.
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Management
Spray Copper oxychloride 0.25%. Add wetting agent such as teepol or sandovit added at
the rate of 1ml/lit of water.
Banana bunchy top: Banana bunchy top virus
Economic Importance
The disease is covered by domestic quarantine regulations. Losses were estimated to be
Rs.4 crores every year and 100% loss occurs if infected suckers are planted.
Symptoms
Subsequent leaving show the same symptoms and are dwarfed. Dark broken bands of green
tissues on the veins, leaves and petioles. Plants are extremely stunted. Leaves are reduced in size
marginal chlorosis and curling. Leaves upright and become brittle. Many leaves are crowded at
the top. Branches size will very small. If infected earlier no bunch will be produced. The
disease is transmitted primarily by infected suckers.
Mode of spread
Secondary spread is through the aphid vector Pentalonia nigronervosa
Management
Select suckers from disease free areas. Control vector by spraying methyl demoton 1
ml/l.or Monocrotophos, 2 ml/l.or Phosphomidon 1 ml / lit. or Injection of Monocrotophos 1 ml /
plant (1 ml diluted in 4 ml). Infected plants are destroyed using 4ml of 2, 4, D (50g in 400 ml of
water).
Infectious chlorosis: Cucumber mosaic virus
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Economic Importance
Infectious chlorosis or heart rot of banana is caused by Cucumber Mosaic Virus (CMV)
has recently become serious, the disease has been recorded from 20 to 80 per cent in Poovan
cultivar.
Symptoms
Chlorotic or yellow linear discontinuous streaks on leaves, upward curling of leaves, twisting
and bunching of leaves at the crown, erectness of newly emerged leaves. Sometimes heart rot
symptom also appear. Diseased plants are dwarf, do not produce bunches. The virus spreads
through infected suckers and aphid vectors -Aphis gossypii
Management
Destroy infected plants. Use disease free suckers. Control vector by spraying systemic
insecticide 0.1%
23

Lecture 04 - Diseases of Grapes
Downy mildew: Plasmopara viticola
Symptoms
Irregular, yellowish, translucent sports on the upper surface of the leaves.
Correspondingly on the lower surface, white, powdery growth on leaves. Affected leaves
become, yellow, brown and gets dried. Premature defoliation. Dwarfing of tender shoots. Brown,
sunken lesions on the stem. White growth of fungus on berries which subsequently becomes
leathery and shrivels. Later infection of berries result in soft rot symptoms. No cracking of the
skin of the berries.
Pathogen
Mycelium is intercellular with spherical haustoria, coenocytic, thin walled and hyaline.
Sporangiophores arise from hyphae in the sub stomatal spaces. It branched at right angle to the
main axis and at regular intervals. Secondary branches arise from lower branches.The sporangia
are thin walled, oval or lemon shaped. The Zoospores are pear shaped, biflagellate and 7 – 9
micron meter. The oospores are thick walled.
Through sporangia by wind, rain etc. As oospores present in the infected leaves, shoots and
berries. Also as dormant mycelium in infected twigs. Optimum temperature: 20-22°C. Relative
humidity: 80-100 per cent.
24

Disease Cycle
Management
Spray Bordeaux mixture 1 % or Metalaxyl + Mancozeb 0.4 %.
Powdery mildew : Uncinula necator
Symptoms
Powdery growth mostly on the upper surface of the
leaves.Malformation and discolouration of affected
leaves. Discolouration of stem to dark brown. Floral
infection results in shedding of flowers and poor fruit set.
Early berry infection results in shedding of affected
berries. Powdery growth is visible on older berries and the infection results in the Cracking of
skin of the berries.
Pathogen
White growth consists of mycelium, conidiophores and conidia. Mycelium is external,
septate and hyaline. Conidiophores are short and arise from external mycelium. Conidia are
produced in chain. They are single celled, hyaline and barrel shaped. The fungus is oidium type.
25

It spread through air-borne conidia. Through dormont mycelium and conidia present in
the infected shoots and buds. Sultry warm conditions with dull cloudy weather, highly
favourable.
Disease Cycle
Management
Spray Inorganic sulphur 0.25 % or Chinomethionate 0.1 % or Dinocap 0.05 %.
Bird’s Eye Spot/Anthracnose: Gloeosporium ampelophagum (Elsinoe amphelina)
Symptoms
The disease appears first as dark red spots on the
berry. Later, these spots are circular, sunken, ashy- gray
and in late stages these spots are surrounded by a dark
margin which gives it the “bird’s-eye rot”
appearance. The spots vary in size from 1/4 inch in
diameter to about half the fruit. The fungus also attacks shoots, tendrils, petioles, leaf veins, and
fruit stems. Numerous spots sometimes occur on the young shoots. These spots may unite and
girdle the stem, causing death of the tips. Spots on petioles and leaves cause them to curl or
become distorted.
Pathogen
Mycelium is septate and dark colored. Conidia single celled oval and hyaline.
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Seed-borne-infected vine, cuttings and air-borne conidia. As dormant mycelium in the
infected stem-cankers. Warm wet weather. Low lying and badly drained soils.
Disease Cycle
Management
Removal of infected twigs.Copper oxychloride 0.2% or Mancozeb 0.25%
27

Lecture 05 - Diseases of Pomegranate and Papaya
Pomegranate
Cercospora fruit Spot: Cercospora sp.
Symptom
The affected fruits showed small irregular black spots, which later on coalesce, into big
spots.
Management
The diseased fruits should be collected and destroyed. Two to three spray at 15 days
interval with Mancozeb 0.25%.
Leaf Spot or Blight: Colletotrichum gloesporioides; Pseudocercospora punicae; Curvularia
lunata and Cercospora punicae)
Symptom
The disease is characterized by appearance of small, irregular and water-soaked spots on
leaves.Affected leaves fall off.
Pathogen
Conidiophores are olivaceous brown, short, fasciculate, sparingly septate. Conidia are
hyaline to pale olivalceous cylindric and septate.
The pathogen spread through wind borne conidia.
Management
Spraying Mancozeb 0.25 % at 15 days interval gives good control of the disease.
Alternaria fruit spot: Alternaria alternata
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Symptom
Small reddish brown circular spots appear on the fruits. As the disease advances these
spots, coalesce to form larger patches and the fruits start rotting. The arils get affected which
become pale and become unfit for consumption.
Management
All the affected fruits should be collected and destroyed. Spraying Mancozeb 0.25 %
effectively controls the disease.
Fruit Rot (Aspergillus foetidus):
The symptoms are in the form of round black spots on the fruit and petiole. The disease
starts from calyx end and gradually the entire fruit shows black spots. The fruit further rots
emitting a foul odour.
Management
The disease can be controlled by spraying of Bavistin (0.5%), Dithane M-45 (0.25%) or
Dithane Z-78 (0.25%) at an interval of 10-15 days from the onset of flowering.
Papaya
Stem rot / Foot rot – Pythium aphanidermatum
Symptoms
29

Water soaked spot in the stem at the ground level which enlarge and griddle the stem.
The diseased area turns brown or black and rot. Terminal leaves turn yellow droop off. The
entire plant topples over and dies. Forward by rain. R. solani is favoured by dry and hit weather. Common
in 2-3 year old trees.
Pathogen
Mycelium is septate, brown and much branched. The sclerotia are black, spherical to
irregular shape and produced in abundance.
Management
Seed treatment with Thiram or Captan 4 g/kg or Chlorothalonil.
Drenching with Copper oxychloride 0.25 % or Bordeaux mixture 1% or Metalaxyl 0.1%.
Powdery mildew – Oidium caricae
Symptoms
While mycelia growth appear on the upper surface of the leaf, flower stalks and fruit.
Seven attak causes yellowing and defiation of leaves.
Pathogen
It is an obligate parasite. The mycelium is hyaline, septate and haustoria develop in
epidermal cells. Conidia are hyaline.
Management
Spray Wettable Sulphur 0.25% or Dinocap 0.05% or Chinomethionate 0.1% or
Tridemorph 0.1%.
Papaya ring spot – Papaya ring spot virus
Symptoms
30

Vein clearing, puckering and chlorophyll leaf tissues lobbing in. Margin and distal parts
of leaves roll downward and inwards, mosaic mottling, dark green blisters, leaf distortion which
result in shoe string system and stunting of plants. On fruits circular concentric rings are
produced. If affected earlier no fruit formation.
Pathogen
The virus particles are rod shaped and thermal inactivation point of the virus lies between
54 and 60˚C.
Mode of spread
Vectored by aphids Aphis gossypii, A. craccivora and also spreads to cucurbits not
through seeds.
Management
Raise papaya seedlings under insect-proof conditions. Plant disease free seedlings. Raise
sorghum / maize as barrier crop before planting papaya. Rogue out affected plants immediately
on noticing symptoms. Do not raise cucurbits around the field.
Leaf curl – Papaya leaf curl virus
Symptoms
Curling, crinkling and distortion of leaves, reduction of leaf lamina, rolling of leaf
margins inward and downward, thickening of veins. Leaves become leathery, brittle and
distorted. Plants stunted. Affected plants does not produce flowers and fruits.
Mode of spread
Spread by whitefly Bemisia tabaci.
Management
Uproot affected plants. Avoid growing tomato, tobacco near papaya. Spraying with
systemic insecticides to control the vector.
Anthracnose – Colletotrichum gloeosporioides
31

Symptom
If affect leaf and stem on erotic spots are produced. On fruit initially brown superficial
discoloration of the skin develops which are circular and slightly sunken. Then they coalesce in
which sparse mycelial growth appear on the margins of a spot. Under humid condition salmon
pink spores are released. Fruits mummified and deformed.
Mode of spread
Infection is caused by fruit from field. Secondary spread by conidia by rain splashes
Management
Spray with Carbendazim 0.1% (or) Chlorothalonil 0.2% or Mancozeb 0.2%.
32

Powdery mildew – Oidium caricae
Symptoms
While mycelia growth appear on the upper
surface of the leaf, flower stalks and fruit. Seven attak
causes yellowing and defiation of leaves.
Pathogen
It is an obligate parasite. The mycelium is hyaline, septate and haustoria develop
in epidermal cells. Conidia are hyaline.
Management
Spray Wettable Sulphur 0.25% or Dinocap 0.05% or Chinomethionate 0.1% or
Tridemorph 0.1%.
Papaya ring spot – Papaya ring spot virus
Symptoms
Vein clearing, puckering and chlorophyll leaf
tissues lobbing in. Margin and distal parts of leaves roll
downward and inwards, mosaic mottling, dark green
blisters, leaf distortion which result in shoe string
system and stunting of plants. On fruits circular concentric rings are produced. If
affected earlier no fruit formation.
Pathogen
The virus particles are rod shaped and thermal inactivation point of the virus lies
between 54 and 60˚C.
Mode of spread
Vectored by aphids Aphis gossypii, A. craccivora and also spreads to cucurbits
not through seeds.
Lecture 06 - Disease of Guava
33

Management
Raise papaya seedlings under insect-proof conditions. Plant disease free seedlings.
Raise sorghum / maize as barrier crop before planting papaya. Rogue out affected plants
immediately on noticing symptoms. Do not raise cucurbits around the field.
Leaf curl – Papaya leaf curl virus
Symptoms
Curling, crinkling and distortion of leaves,
reduction of leaf lamina, rolling of leaf margins inward
and downward, thickening of veins. Leaves become
leathery, brittle and distorted. Plants stunted. Affected
plants does not produce flowers and fruits.
Mode of spread
Spread by whitefly Bemisia tabaci.
Management
Uproot affected plants. Avoid growing tomato, tobacco near papaya. Spraying
with systemic insecticides to control the vector.
Anthracnose – Colletotrichum gloeosporioides
Symptom
If affect leaf and stem on erotic spots
are produced. On fruit initially brown
superficial discoloration of the skin
develops which are circular and slightly
sunken. Then they coalesce in which sparse
mycelial growth appear on the margins of a
spot. Under humid condition salmon pink
spores are released. Fruits mummified and deformed.
Mode of spread
Infection is caused by fruit from field. Secondary spread by conidia by rain
splashes
Management
Spray with Carbendazim 0.1% (or) Chlorothalonil 0.2% or Mancozeb 0.2%.
34

Lecture 06 - Disease of Guava and Sapota
Guava
Anthracnose: Colletotrichum gloeosporioides
Symptoms
Symptoms of this disease are observed on mature
fruits on the tree. The characteristic symptoms consist of
sunken, dark colored, necrotic lesions. Under humid
conditions, the necrotic lesions become covered with pinkish
spore masses. As the disease progresses, the small sunken
lesions coalesce to form large necrotic patches affecting the
flesh of the fruit.
Pathogen
Conidia are hyaline, aseptate, oval to elliptical condiophore is cylindrical.
Acervulli are dark brown to black.
The conidia are spread by wind or rain.
Management
Spray Mancozeb 0.25%.
Guava rust: Puccinia psidii
Symptoms
The pathogen can affect foliage, young shoots,
inflorescences and fruit of guava. Typical symptoms associated
with this disease include distortion, defoliation, reduced
growth and if severe, mortality. On fully expanded leaves, dark
bordered, roughly circular brown lesions with yellow halos
develop.
Management
Control of guava rust is based on the use of fungicides. Scouting fields for onset
of disease or during the times of year when environmental conditions are favorable for
pathogen infection are recommended so that proper and timely fungicide applications can
35

Lecture 07 - Disease of Apple (2 Lectures)
Scab –Venturia inaequalis
Symptoms
Symptom appears on leaves and fruits. On lower side of the leaf lesion appear as
olivaceous spots which turn dark brown to black and become velvety. On young foliage, the
spots have a radiating appearance with a feathery edge. On older leaves the lesions are more
definite in outline. The lesion may form a convex surface with corresponding concave area on
the opposite side. In severe infection leaf blade curved, dwarfed and distorted. Fruits show small,
rough, black circular lesions. The centre of the spots become corky and on mature fruits, yellow
halo is seen around the lesions.
Pathogen
The mycelium is internal. Ascospores are two celled, greenish, grey or yellowish in color.
Pseudothecia formed in autumn and winter mature in spring to produce ascospores, the
chief inoculum for primary infection. The secondary spread is through conidia.
Disease cycle
This disease, caused by the fungus Venturia inaequalis (anamorph Spilocaea pomi), may
be quite severe when rainy, cool weather occurs in the spring. Fungal spores are produced in
early spring on dead, fallen apple leaves about the time buds begin to develop. These spores are
splashed by rain and blown by wind to land on developing plant tissue and initiate infections.
After spots appear on the newly formed leaves, more spores are produced that spread infection to
other parts of the tree. Again, rainy weather greatly encourages spore spread and infection during
the secondary phase of spore production. The fungus over winters on fallen leaves.
36

Clean cultivation, collection and destruction of fallen leaves and pruned materials in
winter to prevent the sexual cycle. Spray Tridemorph 0.1% before flowering. Spray Mancozeb
0.25 % at bearing stage. Spray 5 % urea prior to leaf fall in autumn and 2 % before bud break to
hasten the decomposition of leaves.
S.No Tree stage Fungicide/100lit
1 Silver tip to given tip Captafol 200 gm (or) Captan 300 g or Mancozeb 400 g
2 Pink bud or 15 days after 1 st
spray
Captan 250 g or Mancozeb 300 g
3 Petal fall Carbendazim 50 g
4 10 days later Captan 200 g.or Mancozeb 300g
5 14 days after fruit set Captofol 150 g
Add stickers – teepol or triton 6 ml/10 lit of spray fluid.
Powdery mildew – Podosphaera leucotricha.
37

Symptom
Powdery mildew may be found on buds, blossoms, leaves, twigs, and fruit. In spring,
infected flower buds open 5-8 days later than healthy buds. The buds are killed or distorted.
Symptoms first appear in the spring on the lower surface of leaves, usually at the ends of
branches. Small, whitish felt-like patches of fungal growth appear and quickly cover the entire
leaf. Diseased leaves become narrow, crinkled, stunted and brittle, which results in their drying
out and fall. The fungus spreads rapidly to twigs, which stop growing and become stunted. In
some cases the twigs may be killed back. Leaves and blossoms from infected buds will be
diseased when they open the next spring. Infected blossoms shrivel and produce no fruit. Fruit
symptoms are not usually seen unless the disease has built up to high levels on susceptible
cultivars. The fruit surface may become russetted or discolored, and dwarfed. Heavily mildewed
trees are weakened, and are more susceptible to other pests and winter injury. It is the only
fungal apple disease that is capable of infecting without wetting from rain or dew. In nurseries
the fungus may spread to all developing leaves and cause stunting of vegetative terminal growth.
Pathogen
Powdery mildew is caused by, Podosphaera leucotricha, an ascomycetous heterothallic
fungus. Conidia are ellipsoidal, truncate and hyaline. Perithecia are subglobose, are densely
gregarious, and rarely scattered, and have apical and basal appendages. The asci in the perithecia
are oblong to subglobose. Eight ascospores are present in the ascus. The fungus over winters as
fungal strands (mycelium) in vegetative or fruit buds which were infected the previous season.
The fungus overwinters in the form of mycelium in diseased vegetative buds and fruits.
Secondary spread is through wind borne conidia.
38

Disease Cycle
The mildew fungus over winters mainly as mycelium in dormant blossom and shoot buds
produced and infected the previous growing season. Conidia are produced and released from the
unfolding leaves as they emerge from infected buds at about tight cluster stage. Conidia
germinate in the high relative humidity usually available on the leaf surface at 10-25˚C with an
optimum of 19-22˚C. Germination does not occur in free moisture. Early-season mildew
development is affected more by temperature than by relative humidity. Abundant sporulation
from over wintering shoots and secondary lesions on young foliage leads to a rapid buildup of
inoculum. Secondary infection cycles may continue until susceptible tissue is no longer
available. Since leaves are most susceptible soon after emergence, infection of new leaves may
occur as long as shoot growth continues. Fruit infection occurs from pink to bloom. Over
wintering buds are infected soon after bud initiation. Heavily infected shoots and buds are low in
vigor and lack winter hardiness, resulting in a reduction of primary inoculum at temperatures
below -24˚C.
39

Management:
Spray Dinocap 0.05% or Chinomethionate 0.1%
Fire blight- Erwinia amylovora
Symptom
The initial symptom usually occurs on leaves, which become water soaked, then shrivel turn
brownish to black in colour and fall or remain hanging in tree. The symptom spread to twigs.
Terminal twigs wilt from tip to downward and also spread to branches.Fruits becomes water
soaked, turns brown, shrivels and finally becomes black. Oozing may be seen in the affected
area.
Pathogen
The bacterium is rod shaped and motile by peritrichous flagella. Bacterium occurs
usually singly but pairs or chais of 3 of 4 bacteria also exist. Each bacterial cell is enclosed in a
capsule.
The bacterium overwinters at the margin of cankers formed during previous season. They
survive most often in large branches and seldom in twigs less than 1 cm in dia. Flies, Wasps and
honey bees and rain splashes spread the bacteria into freshly wounded tissues inside the leaf.
Young tender twigs are infected by bacteria through their lenticels, through wounds made by
various agents and through insects carrying bacteria and feeding on the twigs.
40

Disease Cycle
Management
Removal and destruction of affected parts. Removal of blighted twigs. Spray with
Streptomycin 500 ppm.
Soft rot – Penicillium expansum
Symptom
Young spots starts from stem end of the fruit as light brown watery rot. As the fruit
ripens area of the rotting increases, skin becomes wrinkled. A peculiar musty odour is emitted
41

under humid condition a bluish green sporulating growth appears. Infection take place by
wounds in the skin caused by insects and during handing in storage and transport.
Pathogen
Conidiophores give rise to 1-3 main branches. They in turn produce crowdwd whorls of
branchlets. Conidia are formed in chains. Conidia are green or bluish green in mass.
The fungal spores are spread by air. Mycelium can infect through bruisedor wounded
fruits in close contact. Infection of the fruit usually take place through wounds in the skin, such
as wounds caused by insect bites, careless picking, rough handling during washing, grading ,
packing, transit and storage. Infection is also through lenticels.
Disease cycle
Spores of the soft rot fungus are present almost everywhere and can survive long periods
of unfavorable conditions. Bulk bins, field crates, pack house lines, and storage rooms are
usually contaminated. Injuries to fruit, especially during picking and handling operations, are the
primary points of entry. At ordinary temperatures, infected fruit can rot in 2 weeks or less.
Management
Careful handling of fruits without causing any wounds. Dipping the fruits aureofunginsol
@ 500 ppm for 20 min gives best control.
Bitter rot – Glomerella cingulata
Symptom
Faint, light brown discolouration beneath the skin develops. The discolouration expands in a
cone shape. The circular, rough lesions become depressed. The lesions increased and covers
entire areas of fruits. Diny black dots appear beneath the cuticle which gives rise to acervuli .
Pink masses of spores are found arranged in defined rings.
42

Disease Cycle
The fungus over winters in mummified fruit, in cracks and crevices in bark, and in cankers
produced by the bitter rot fungus or by other diseases, such as fire blight. Jagged edges of broken
limbs are also ideal sites. The bitter rot fungus is one of the few rot organisms that can penetrate
unbroken skin of fruit. Although penetration is direct, wounds can be colonized rapidly by the
fungus. Spores are waterborne and are released during rainfall throughout the growing season.
Fruit infection can occur early but is more common from mid to late season. Often, the first
infections appear in cone-shaped areas within the tree beneath mummies or a canker. Factors
which determine the time of appearance of bitter rot are the maturity of fruit, temperature and
humidity, and the presence of disease in the area. The optimum conditions for disease
development include rainfall, relative humidity of 80 to 100 percent, and warm temperatures.
Infection can occur in as little as five hours at 26˚C.
Management
Spray Mancozeb 0.25 % in field. Treatment with Mancozeb 0.25 % to check the disease
in storage.
43

Lecture 08 - Diseases of Chilli
Damping off: Pythium aphanidermatum
Symptoms:
Seedlings killed before emergence. Water soaking and shrivelling of stem. Factors
favouring infection:Moist soils poordrainage 90-100% R.H soil temperature 20°C.
Pathogen
Mycelium is hyaline, coenocytic and zoosporangia are lobed and branched. Zoospores
are biflagellate and oogonia are spherical with smooth walled.Antheridia are monoclinous,
intercalary or terminal. Oospores are aplerotic, single with thick wall.
The pathogen is soil borne. Zoospores spread through irrigation water. The disease
spreads to main field by planting infected seedlings.
Management
Soil drenching with Copper oxychloride 0.25%
Fruit Rot and Die Back- Colletotrichum capsici
Symptoms:
44

As the fungus causes necrosis of tender twigs from the tip backwards the disease is called
die-back Infection usually begins when the crop is in flower. Flowers drop and dry up. There is
profuse shedding of flowers. The flower stalk shrivel and dry up. This drying up spreads from
the flower stalks to the stem and subsequently causes die-back of the branches and stem and the
branches wither. Partia1lly affected plants bear fruits which are few and of low quality. On the
surface of the soil the necrotic areas are found separated from the healthy area by a dark brown
to black band.
Pathogen
The mycelium is septate and inter and intra cellular. Conidia in mass appear pinkish.
They are borne singly at the tip of conidiophores.
The fungus is seed borne and the secondary infection is by air borne conidia ans also by
rain. The disease spreads rapidly by wind blown rains during rainy season. Flies and other
insects are found responsible for dissemination of the spores from one fruit to another. The
fungus may not survive long in soil, but may survive on the dead twigs stored under dry
conditions. Seeds from badly diseased fruits may also carry the primary inoculum.
Management
Use of disease-free seeds is important in preventing the disease. Seed treatment with
Thiram or Captan 4g/kg is found to be -effective in eliminating the seed-borne inoculum. Good
control of the disease has been reported by three sprayings with Ziram O. 25% Captan 0.2% or
miltox 0.2%. Chemicals like wettable sulphur 0.2%, copper oxychloride 0.25% and Zineb 0.15%
not only reduced the disease incidence but also increased the yield of fruits. The first spraying
should be given just before flowering and the second at the time of fruit formation. Third
spraying may be given a fortnight after second spraying.
Powdery mildew: Leveillula taurica
Symptoms
45

Shedding of foliage. White powdery growth on lower side of leaves.
Disease cycle
The powdery mildew disease cycle (life cycle) starts when spores (known as conidia) land on
a chilli leaf. Spores germinate much like a seed and begin to grow into the leaf. chilli powdery
mildew parasitizes the plant using it as a food source. The fungus initially grows unseen within
the leaf for a latency period of 18-21 days. Then the fungus grows out of the breathing pores
(stomates) on the under surface of the leaf, producing spores which are borne singly on
numerous, fine strands or stalks (conidiophores). These fungal strands become visible as white
patches or mildew colonies on the under side of the leaf. Repeated cycles of powdery mildew
can lead to severe outbreaks of powdery mildew that economically damage the crop.
Management
Spray Wettable sulphur 0.25% or Dinocap (Karathane) 0.05%
Bacterial leaf spot: Xanthomonas campestris pv. vesicatoria
Symptoms
46

The leaves exhibit small circular or irregular, dark brown or black greasy spots. As the spots
enlarge in size, the centre becomes lighter Surrounded by a dark band of tissue. The spot
coalesce to form irregular lesions. Severely affected leaves become chlorotic and fall off.
Petioles and stems are also affected. Stem infection leads to formation of cankerous growth and
wilting of branches. On the fruits round, raised water soaked spots with a pale yellow border and
produced. The spots turn brown developing a depression in the centre wherein shining droplets
of Bacterial cozen may be observed.
The disease is primarily seed borne. It spreads in the nursery and is further disseminated
with infected transplants. Spattering rains are the chief means of dissemination. The bacterium
subsists in infected debris.
Management
Seed treatment with 0.1% mercuric chloride solution for 2 to 5 minutes is effective.
Seedlings may be sprayed with Bordeaux mixture 1. Per cent or copper oxychloride 0.25%.
Spraying with streptomycin should not be done after fruits begin to form. Field sanitation is
important. Also seeds must be obtained from disease free plants.
Cercospora leaf spot :Cercospora capsici
Symptoms
Leaf lesions typically are brown and circular with small to large light grey centers and dark
brown margins. The lesions may enlarge to 1cm or more in diameter and some times coalesce.
Stem, petiole and pod lesions also have light grey centers with dark borders, but they are
typically elliptical. Severely infected leaves drop off prematurely resulting in reduced yield.
Pathogen
Stromata are well developed. Conidiophores are 30- 60 x 4.5 – 5.5 micron meter. Conidia
are subhyaline to coloured, acicular to obculate.
47

Primary source of infection are infected seeds, volunteer plants and infected plant debris.
Secondary spread is through air borne conidia.
Management
Spray twice at 10-15 days interval with Mancozeb 0.25% or Chlorothalonil (Kavach)
0.1%.
Fusarium wilt :Fusarium oxysporum f.sp.capsici
Symptoms
Fusarium wilt is characterised by wilting of the plant and upward and inward rolling of the
leaves. The leaves turn yellow and die. Generally appear localised areas of the field where a high
percentage of the plants wilt and die, although scattered wilted plants may also occur. Disease
symptoms are characterised by an initial slight yellowing of the foliage and wilting of the upper
leaves that progress in a few days into a permanent wilt with the leaves still attached. By the time
above - ground symptoms are evident, the vascular system of the plant is discoloured,
particularly in the lower stem and roots.
Pathogen
Mycelium is grayish white. Microconidia are formed singly, hyaline and cylindrical.
Macro conidia are cylindrical to falcate. Chlamydospores are globose to oval and rough walled.
Management
Use of wilt resistant varieties. Drenching with 1% Bordeaux mixture or Blue copper or
Fytolan 0.25% may give protection.· Seed treatment with 4g Trichoderma viride formulation or
2g Carbendazim per kg seed is effective. Mix 2kg T.viride formulation mixed with 50kg FYM,
48

sprinkle water and cover with a thin polythene sheet. When mycelia growth is visible on the heap
after 15 days, apply the mixture in rows of chilli in an area of one acre.
Leaf curl
Leaves curl towards midrib and become deformed. Stunted plant growth due to shortened
internodes and leaves greatly reduced in size. Flower buds abcise before attaining full size and
anthers do not contain pollen grains. The virus is generally transmitted by whitefly. So control
measures of whitefly in this regard would be helpful.
Mosaic Viruses
Light green and dark green patches on the leaves. Stunted plant growth during early
stages. Yellowing, chlorotic ring spots on leaves and fruits.
Management of viral diseases
Control measures are not known for majority of viral diseases. Hence, mechanical, cultural
methods are mostly recommended. The infected plants should be uprooted and burnt or buried to
avoid further infection. Avoid monoculture of chilli crop. Selection of healthy and disease - free
seed. Suitable insecticidal sprays reduce the incidence of viral diseases, since majority of viral
diseases are transmitted by insect vectors. Soaking seeds in a solution containing 150 g
Trisodium orthriphosphate per litre of water for 30 minutes inhibits seed - borne inoculum.
Treated seed should be washed with fresh water and dried before sowing. Nursery beds
should be covered with nylon net or straw to protect the seedlings from viral infection. Raise 2-3
rows of maize or sorghum as border crop to restrict the spread of aphid vectors. Apply
Carbofuran 3G @ 4-5 Kg/acre in the mainfield to control sucking complex and insect vectors
selectively. If it is not possible spray the crop with systemic insecticides. Like Monocrotophos
1.5 ml or Dimethoate 2ml of Acephate 1g per litre of water. Collect and destroy infected virus
plants as soon as they are noticed.
Bacterial soft rot -Erwinia carotovora subsp. Carotovora
Symptoms
49

The fleshy fruit peduncle is highly susceptible and is frequently the initial point of infection.
Both ripe and green fruit may be affected. Initially, the lesions on the fruit are light to dark-
colored, water-soaked, and somewhat sunken. The affected areas expand very rapidly,
particularly under high temperatures, and tissues lose their texture. In later stages, bacterial ooze
may develop from affected areas, and secondary organisms follow, often invading the rotted
tissue. Post-harvest softening of stem end of fruit. The affected fruit hang from the plant like a
water-filled bag.
Conditions for Disease Development
The bacteria may persist in fields where peppers are rotated with other susceptible crops
such as cabbage and potato. The bacteria may be present as a contaminant on the surface of
pepper seed. The bacteria can be transmitted by drainage water, irrigation water, or by sprinkler
irrigation, but a wound is necessary for infection to occur. Wounding often arises from rough
handling of plants during weeding, or due to a strong wind, or from insect feeding. European and
Asiatic corn borers may introduce bacteria into the fruit peduncle of pepper during feeding. A
high rate of nitrogen fertilization is associated wit increased susceptibility to soft rot. Warm,
moist weather is also highly favorable for infection.
Management
Use chlorinated wash water to reduce populations of soft rot bacteria and to reduce the
risk of infection during washing. This will not reduce soft rot development in fruit infected
with the bacterium prior to harvest. Allow fruit to dry thoroughly. During packing and storage,
the fruit should be kept clean and maintained in a cool, dry place
Alternaria Rot- Alternaria sp.
Symptoms
The fungus is reported to enter wounds (sunscald or punctures). Dusty black spores on
fruit spots are characteristic. In most instances this disease follows blossom-end rot, but it also
follows injuries, chilling, and other decays. On the fruit, large greenish-brown to brown lesions
covered, with grayish-brown mold are produced. Similar lesions on the lower-part of the fruit are
characteristic of Alternaria rot following blossom-end rot. The larger lesions may show
50

alternating light and dark-brown concentric zones. Shipping peppers under standard refrigeration
will check the development of this rot, but when the fruit is removed from refrigeration the decay
will advance rapidly at moderate to warm temperatures.
Pathogen
Hyphae are septate, branched, light brown becoming darker with age and inter and intra
cellular. Conidiophores emerge through stomata. Conidia are single and muriform.
Infected seeds, volunteer plants and infected plant debris are primary source of infection.
Management
Pre storage dry heat
The effectiveness of a prestorage dry heat treatment and hot water dip in reducing storage
rots of capsicum caused by Alternaria alternata. Treatment with hot air at 38˚C for 48-72 h or
hot water at 50˚C to 53˚C for 2 to 3 min, resulted in reduction in the pathogenicity and
development of these pathogens in inoculate peppers.
51

Lecture 09 - Diseases of Brinjal
Bacterial Wilt: Pseudomonas solanacearum
Symptoms
Bacterial wilt symptoms on leaf surface Wilting, stunting, yellowing of the foliage and
finally collapse of the entire plant are the characteristic symptoms of the disease. Lower leaves
may droop first before wilting occurs. The vascular system becomes brown. Bacterial ooze
comes out from the affected parts. Plant show wilting symptoms at noontime will recover at nights, but die
soon.
Pathogen
The bacterium is non acid fast, non spore forming, non capsulated and motile by a polar
flagellum. The bacterium produces acid but no gas in dextrose, sucrose, lactose and glycerol.
Starch hydrolyzed with slight liquefaction of gelatin.
The bacterium infects banana, chillies, fennel, ginger, potato, radish, tomato etc., the
bacterium though a non spore former is found to be alive and viable for more than 16 months
under laboratory conditions. The pathogen is found to be alive in the infected plant debris for
about 10 months. Presence of root knot nematode, Meloidogyne javanica increases the wilt
incidence.
Management
Use resistant variety .Crop rotation with cruciferous vegetables such as cauliflower help
in reducing the disease incidence. Fields should be kept clean and effected parts are to be
collected and burnt. Spray Copper fungicides to control the disease (2% Bordeaux mixture.). The
disease is more prevalent in the presence of root knot Nematodes, so control of these nematodes
will suppress the disease spread.
52

Cercospora Leaf Spot :Cercospora solani -melongenae, C. solani
Symptoms
The leaf spots are characterized by chlorotic lesions, angular to irregular in shape, later
turn grayish-brown with profuse sporulation at the centre of the spot. Severely infected leaves
drop off prematurely, resulting in reduced fruit yield.
Pathogen
The fungus produces stromata which are globular. Conidiophores in mass are medium
dark and slightly olivaceous brown in colour and paler towards the tip. Conidia are sub hyaline
to pale olivaceous.
The disease is spread by air borne conidia.
Management
Pant Samrat variety is resistant to both the leaf spots. Diseases can be managed by
growing resistant varieties. Spraying 1 per cent Bordeaux mixture or 2 g Copper oxychloride or
2.5 g Zineb per litre of water effectively controls leaf spots.
Alternaria leaf Spot :Alternaria melongenae, A. solani
Symptoms
Cracks appearing in leaf spot. The two species of Alternaria occur commonly, causing
the characteristic leaf spots with concentric rings. The spots are mostly irregular, 4-8 mm in
diameter and may coalesce to cover large areas of the leaf blade. Severely affected leaves may
53

drop off. A. melongenae also infects the fruits causing large deep-seated spots. The infected
fruits turn yellow and drop off prematurely.
Pathogen
Mycelium is septate, branched, light brown to dark brown. It is inter and intra cellular.
Conidiophores emerge through stomata and dark colored. Conidia are single celled, muriform,
beaked and produced in chains. The conidia are with 5-10 transverse septa and a few longitudinal
or oblique septa.
The disease is spread by wind borne conidia.
Management
Spraying 1 per cent Bordeaux mixture or 2 g Copper oxychloride or 2.5 g Zineb per litre
of water effectively controls leaf spots.
Little Leaf of Brinjal
Economic Importance
This disease of brinjal was reported from India in 1938 and as far as known it occurs only
in India and Sri Lanka. In almost all the states of the country it has become a serious problem
facing brinjal cultivation. The yield loss is hundred per cent in the diseased plants.
Symptom
The characteristic symptom is the smallness of the leaves. The petioles are so short and
the leaves appear to be sticking to be stem. Such leaves are narrow, soft, smooth and yellow.
Newly formed leaves are much more shorter. The internodes of the stem are also shortened.
54

Axillary buds get enlarged but their petioles and leaves remain shortened. This gives the plant a
bushy appearance. Mostly, there is no flowering but if flowers are formed they remain green.
Fruiting is rare.
Pathogen
Little leaf was first considered a disease caused by a virus. In 1969 it was attributed to a
mycoplasma-like organism, closely related to aster-yellows and curly top.
It is a sap transmissible disease. The organism has been transmitted to Datura, tomato and
tobacco. It occurs in nature on Datura fastuosa and Vinca rosea. Natural transmission is through
a vector, Cestius phycytis (Eutettix phycytis) while Empoasca devastans is a less effective vector.
Perennation of the organism is through its weed hosts.
The disease is transmitted by leaf hoppers, Hishimonas phycitis and Empoasca devastans
and grafting. E. devastans is less effective vector. Perennation of virus is through weed host.
This disease has a very wide host range.
Management
The severity of the disease can be reduced by destruction of affected plants and spraying
of insecticides. New crop should be planted only when diseased plants in the field and its
neighbourhood have been removed.
Methyldemeton 25 EC 2 ml / litre
Dimethoate 30 EC 2 ml/ litre
Malathion 50 EC 2 ml/litre
has been recommended for vector control.
Although mycoplasmas are reported to be suppressed by tetracyclines field application
of this method has not yet been recommended. Varietal resistance has not been systematically
studied. Cultivars such as Pusa Purple Cluster, Arka Sheel, Aushy, Manjari Gota and Banaras
Giant show moderate resistance to resistance in the field. Other cultivars found tolerant to the
disease are Black Beauty, Brinjal Round and Surati.
Damping off: Pythium aphanidermatum, Pythium indicum, , Phytophthora parasitica,
Rhizoctonia solani and Sclerotium rolfsii.
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Symptom
Sudden collapsing of the seed lings occur in the seed bed. The seedlings are attacked at
the collar region and the attacked seedlings are toppled down. The disease spreads through fungi
present in the soil. The disease spreads through fungi present in the soil.
Management
The disease can be controlled by seed treatment with agrosan or ceresin @2gm/kg of
seed.
Tobacco mosaic virus (TMV)
Symptoms
Mosaic mottling of leaves and stunting of plants are the characteristic symptoms of potato
virus Y Mosaic symptoms are mild in early stages but later become severe. Infected leaves are
deformed, small and leathery. Very few fruits are produced on infected plants. The important
symptom produced by tobacco mosaic virus is conspicuous mottling of leaves. Leaves also
develop blisters in advanced cases. Severely infected leaves become small and misshapen. Plants
infected early remain stunted. PVY is easily sap transmitted.
It is transmitted in the field through aphids, Aphis gossypii and Myzus persicae and
perpetuates on weed hosts like Solanum nigrum and S.xanthocarpum. TMV is transmitted by
sap, contaminated implements and clothes, soil debris and hands of labour. It can perpetuate on many
cultivated plants like cucurbits, legumes, pepper, tobacco, tomato and weed hosts. The virus survives in plant debris
in soil.
Management
Destroy all weeds and avoid planting cucumber, pepper, tobacco, tomato near brinjal
seed beds and field. Wash hands with soap and water before working in seed beds. Prohibit
smoking or chewing of tobacco who are handling brinjal seedlings. Spray insecticides like
Dimethoate 2 ml/litre or Metasystox 1 ml/litre of water to control the insect vectors.
Collar rot :Sclerotium rolfsii
Symptoms
The disease occasionally occurs in serious form. The lower portion of the stem is affected
from the soil borne inoculum (sclerotia). Decortications is the main symptom. Exposure and
necrosis of underlying tissues may lead to collapse of the plant. Near the ground surface on the
stem may be seen the mycelia and sclerotia. Lack of plant vigour, accumulation of water around
the stem, and mechanical injuries help in development of this disease.
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Management
Seed treatment with 4 g of Trichoderma viride formulation per kg seed will help in
reducing the disease. Spraying with Mancozeb @ 2g/Litre of water. Collection and destruction of
diseased parts and portions of the plant.
Fruit rot :Phomopsis vexans
Symptoms
Affects all above the ground plant parts. Spots generally appear first on seedling stems or
leaves. Girdle seedling stems and kill the seedlings. Leaf spots are clearly defined, circular, up to
about 1 inch in diameter, and brown to gray with a narrow dark brown margin. Fruit spots are
much larger, affected fruit are first soft and watery but later may become black and mummified.
Center of the spot becomes gray, and black pycnidia develop.
Pathogen
Pycnidia with or without beak are found in the affected tissue. They are globose or
irregular. Conidiophores in the pycnidium are hyaline, simple or branched. Conidia are hyaline,
one celled and sub cylindrical. Ascospores are hyaline, narrowly ellipsoid to bluntly fusoid with
one septum.
The fungus survives in the infected plant debris in the soil. It is seed borne. The spores
are spread by rain splashes. The fungus spreads through implements and insects.
Management
Seeds should be dipped in hot water at 50˚C for 30 min. spraying with difolation 0.2% or
captan 0.2% in the nursery and field at 7 – 10 days interval controls the disease. Deep summer
ploughing, three year crop roation and collection and destruction of diseased plant debris are
some of the other control methods. Spraying the crop in the field with zineb 0.2% or Bordeaux
mixture 0.8% is effective in controlling Phomopsis blight.
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Lecture 10 - Diseases of Bhendi
Bhendi
Cercospora Leaf Spots:Cercospora malayensis,
C. abelmoschi
Symptoms
In India, two species of Cercospora produce leaf spots in bhendi. C. Malayensis causes
brown, irregular spots and C. abelmoschi causes sooty black, angular spots.Both the leaf spots
cause severe defoliation and are common during humid seasons.
Pathogen
Conidiophores are pale to medium olivaceous brown, multiseptate, some times branched,
geniculate and irregular. Conidia are obclavate to cylindric, olivaceous brown and straight to
curved.
The fungus survives in the diseased crop material.
Management
Spraying Mancozeb 0.25 % control the disease.
Fusarium wilt: Fusarium oxysporum f.sp. vasinfectum
Symptoms
The conspicuous symptom is a typical wilt, beginning with a yellowing and stunting of
the plant, followed by wilting and rolling of the leaves as if the roots were unable to supply
sufficient water. Finally, the plant dies. If a diseased stem is split lengthwise, the vascular
bundles appear as dark streaks. When severely infected, nearly the whole stem is blackend.
Pathogen
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Macroconidia are 3- 5 septate formed on sporodochia and pionnotes. In mass conidia
appear buff or salmon orange in color. Macroconidia are fusiform and curved inward at both
ends. The base is pedicellate. Microconidia are septate. Terminal and intercalary chlamydospores
are broadly ovate.
The fungus is soil borne.
Management
Treat the seeds with Mancozeb @ 3g/kg seed. Drench the field with Copper oxy chloride
@ 0.25%.
Powdery mildew: Erysiphecichoracearum
Symptoms
Powdery mildew is very severe on bhendi. Greyish powdery growth occurs on the under
as well as on the upper surface of the leaf causing severe reduction in fruit yield.
Pathogen
Conidia are single celled, hyaline, barrel shaped and in long chains. Cleistothecia are
globose and dark brown myceloid appendages. The asci are pedicellate, ovate or ellipsoid. The
number of ascospores is usually 2 rarely 3 per ascus. The ascospores are single celled, hyaline
and oval to sub cylindrical
Management
Spary inorganic sulphur 0.25% or Dinocap 0.1% 3 or 4 times at 15 days interval.
Vein-Clearing/Yellow Vein Mosaic :Bhendi yellow vein mosaic virus
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Symptoms
Yellowing of the entire network of veins in the leaf blade is the characteristic symptom. In
severe infections the younger leaves turn yellow, become reduced in size and the plant is highly
stunted. The veins of the leaves will be cleared by the virus and intervenal area becomes
completely yellow or white. In a field, most of the plants may be diseased and the infection may
start at any stage of plant growth. Infection restricts flowering and fruits, if formed, may be
smaller and harder. The affected plants produce fruits with yellow or white colour and they are
not fit for marketing.
Pathogen
The virus particles are 16 – 18nm in diameter.
Mode of spread
The virus is spread by whitefly.
Management
By selecting varieties resistant to yellow vein mosaic like Parbhani Kranti, Arka Abhay,
Arka Anamika, and Varsha Uphar, the incidence of the disease can be minimised. The virus is
transmitted by the whitely (Bemisia tabaci,. Parbhani Kranti, Janardhan, Haritha, Arka Anamika
and Arka Abhay can tolerate yellow vein mosaic. For sowing during the summer season, when
the whitefly activity is high, the susceptible varieties should be avoided. Spraying
monocrotophos 1.5 ml/litre of water can restrict the disease spread. Synthetic pyrethroids should
not be used because it will aggravate the situation. It can be controlled by application of
Chlorpyriphos 2.5 ml + neem oil 2 ml lit of water.
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Phoma canker (Phoma exigua)
Water soaked lesion appear on fruits. Black spots with irregular margin Black area -
pycnidial formation. 80-90% fruit loss post harvest rot of okra pods rhizoctonia solani in brazil.
Completely rotted, the pod's typical greenish color turning brown and the infected tissues fully
covered with mycelia. Internally, immature seeds and placenta infected. Diseased tissues were
light brown to black. Externally, mycelia tend to be fluffy and lighter in color, forming a large
number of dark sclerotia on the fruit surface.
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Lecture 11 - Diseases of Potato (2 Lectures)
Late blight of potato: Phytopthora infestans
Symptom:
It affects leaves, stems and tubers. Water soaked spots appear on leaves, increase in size,
turn purple brown& finally black colour White growth develops on under surface of leaves. This
spreads to petioles, rachis& stems. It frequently develops at nodes. Stem breaks at these points
and the plant topples over. In tubers, purplish brown spots and spread to the entire surface on
cutting, the affected tuber show rusty brown necrosis spreading from surface to the center.
Pathogen
The mycelium is endophytic, coenocytic and hyaline which are inter cellular with double
club shaped haustoria type. Sporangiophores are hyaline, branched intermediate and thick
walled. Sporangia are thin walled, hyaline, oval or pear shaped with a definite papilla at the apex.
The sporangium may act as a conidium and germinate directly to form a germ tube. Zoospores
are biflagellate possess fine hairs while the other does not.
The infected tubers and the infected soil may serve as a source of primary infection. The
diseased tubers are mainly responsible for persistence of the disease from crop to crop. The air
borne infection is caused by the sporangia.
RH->90% , Temp.-10-25°C and Night temperature:10°C. Cloudiness on the next day
Rainfall at least 0.1mm, the following day.
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Management
A regular spraying and dusting during the growing season give effective control. First
spraying should be given before the commencement of the disease and subsequent should follow
at reqular interval of 10 -15 days. Protective spraying with mancozeb or zineb 0.2 % should be
done to prevent infection of tubers. Destruction of the foliage few days before harvest is
beneficial and this is accomplished by spraying with suitable herbicide. Tuber contamination is
minimized if injuries are avoided at harvest time and storing of visibly infected tubers before
storage. The resistant varities recommended for cultivation are Kufri Naveen, Kufri Jeevan,
Kufri Alenkar, Kufri Khasi Garo and Kufri Moti.
Early blight: Alternaria solani
Symptoms
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It is present in both hills & plains. Brown-black necrotic spot-angular, oval shape
characterized by concentric rings .Several spot coalesce & spread all over the leaf. Shot holes on
fruits.
Pathogen
Hyphae are light brown or olivaceous which become dark coloured with age. The hyphae
are branched, septate and inter and intra cellular. The coniophores emerge through the stomata or
between the epidermal cells. The conidia are club shaped with a long beak which is often half the
long of the whole conidium. The lower part of the conidium is brown while the neck is colorless.
The body of the conidium is divided by 5 – 10 transverse septa and there may or may not be a
few longitudinal septa.
Favourable condition
Dry warm weather with intermittent rain .Poor vigor. Temperature: 25-30°C. Poorly
manured crop.
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The conidia and the mycelium in the soil or in the debris of the affected plants can remain
viable for more than 17 months. These conidia or the new conidia found on the overwintered
mycelium bring about the primary infection of the succeeding potato crop. Secondary infection is
more important in the spread of the disease. The conidia formed on the spots developed due to
primary infection are disseminated by wind to long distances. The conidia from the affected
plant may also be disseminated to the adjoining plants by rain and insects.
Management
Disease free seed tubers should be used for planting. Removal and destruction of infected
plant debris should be done because the spores lying in the soil are the primary source of
infection. Very early spraying with Zineb or captan 0.2% and repeating it for every 15 – 20 days
gives effective control. The variety Kufri Sindhuri possesses a fair degree of resistance.
Post-harvest tuber rots - Sclerotium rolfsii
Symptoms
Wilting is the initial symptom. Yellowish brown coloured Sclerotia appeared on the
infected tuber. Rotting of the tuber. Milky white and floccose appearance of the tuber.
Pathogen
The mycelium is silky white and floccose. It is comprised of septate and branched
hyphae. The branching take place just below the septum. The cells are large in size. Sclerotia of
the fungus are white to begin with and become clove brown at maturity. They are globose and
smooth surfaced.
Favorable condition
Optimum temperature 30-35ºC. Alternate period of wet and dry soil condition.
The mycelium and sclerotia of the organisam subsist in the soil and are responsible for
the infection of the crop. The pathogen is disseminated with infected soil, in running water and
on farm implements. Mycelium and sclerotia may also be carried to soil with the seed tubers. In
dry soil scleritia can remain viable for more than two years.
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Management
Treating seeds with mercury compounds after harvest reduces tuber rot. Treating the
furrows at planting with PCNB @ 15kg/ ha reduces the disease icidence.Cultural practices like
heavy earthing and irrigation at regular intervals can also check the disease. The disease is low in
the variety Kufri Sindhuri. Among the Indian commercial cultivars, Kufri Bahar, Kufri
Chamatkar, Kufri Jyothi, Kufri muthu and Kufri swarna are resistant. The disease can be
controlled to a certain extent by growing non susceptible crops like corn and sorghum.
Black scurf- R. solani
Symptoms
Black speck, black speck scab, russet scab on tubers. At the time of sprouting dark brown
colour appear on the eyes. Affected Xylem tissue causes to wilting of plants. Infected tuber
contains russeting of the skin. Hard dry rot with browning on internal tissue. Spongy mass
appear on the infected tuber. Seed tubers are source of spread. Moderately cool, wet weather and
temp 23 °C are the favourable for the development of disease.
Pathogen
The mycelium is hyaline when young and brown at maturity. Hyphae are septate and
branched with a characteristic constriction at their junction with the main hyphae. The branches
arise at a right angle to main axis. Sclerotia are black. A basidium bears four sterimata each with
a basidiospore at the end. The basidiospores are hyaline, elliptical to obovate and thin walled.
They are capable of forming secondary basidiospores.
The fungus is capable of leading a saprophytic life on the organic material and can
remain viable in the soil for several years. The sclerotia on the seed tubers is the principal source
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of infection of the subsequent crop raised with these tubers. On return of favourable conditions
the mycelium present in the soil may develop producing new hypae.
Management
Disease free seed tubers alone should be planted. If there is a slight infection of black
scurf that can be controlled by treating seed tubers with mercuric chloride solution for 1.5 hr
with acidulated mercuric chloride solution for 5 min. Treating the soil with pentachloroni
trobenzene at the rate of 70 kg/ ha lowers the incidence of the disease, but it is too expensive and
cumbersome. Well sporulated tubrs may be planted shallow to control disease. The disease
severity is reduced in the land is left fallow for 2 years.
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Common scab or corkey scab – Streptomyces scabies
Symptoms
Corkiness of the tuber periderm is the characteristics symptoms. 1/4 inch into the tuber
surface are russette appearance. Slightly pitted on the infected tuber. Light brown to dark brown
lesion appears on the infected tuber. Affected tissue will attract insects.
Pathogen
Aerial mycelium in pure culture has of prostrate branched threads. Sporogenous hyphae
are spiral in form. Conidia are produced by the formation of septa at intervals along the hyphae,
which contract to form narrow isthmuses between the cells. Conidia are roughly cylindrical and
hyaline. The conidia can germinate even at higher temperatures. The growth of the organisam is
good in slightly alkaline medium and is checked at pH 5.2.
It attacks cabbage, carrot, egg plant, onion, radish, spinach and turnip. The causal
organism perpetuates in soil and infects the crop every year. Infected potato tubers serve as the
main source of long distance spread of the disease. The pathogen may survive passage through
digestive tract of animals and hence it may spread with farm yard manure.
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Disease Cycle
Management
Only scab free seed potatoes should be planted as this will help in checking the spread of
the inoculum and infection to be subsequent crop. Infection of the seed tubers can be removed by
1.5hrs dip in mercuric chloride 0.1% solution or by 2h dip in 1 part formaldehyde in 240 parts of
water. This disease can be reduced by soil application of PCNB at the time of planting. Four to
six years crop roation with alfalfa satisfactory under irrigated conditions. The disease incidence
can be effectively reduced by green manuring the fields before planting potatoes. Common scab
is severe in alkaline soil and application of alkaline fertilizers like calcium ammonium nitrate
should be avoided.
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Brown rot or Bangle blight -Ralstonia solanacearum
Symptoms
At the time tuber formation wilt is the main characteristic symptom. In leaf symptom -
wilt, stunt and yellowing. Browning of xylem tissue. Eye buds are black in colour. Bacteria ooze
coming on infected tuber surface and emits a foul odour.
Pathogen
G –ve, short rod, 1-4 flagella. Colonies are white to brown in colour
Favourable condition
Temp 25to 35ºC , RH above 50 % and PH 6.2-6.6 favours for the development of disease.
Acid soil is not favourable.
Infected soil and seed tubers form the main source of the primary infection. Brown rot
affected plant parts decay and release masses of bacteria in the soil where these may remain
viable from season to season. The bacteria in the soil are disseminated by wind from one field to
the other. The infection usually occurs through wounds in the root system.
Disease cycle
R. solanacearum is a soilborne and waterborne pathogen; the bacterium can survive and
disperse for various periods of time in infested soil or water, which can form a reservoir source
of inoculum. In potato, the brown rot pathogen is also commonly tuber borne. The bacterium
usually infects potato plants through the roots (through wounds or at the points of emergence of
lateral roots).
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Under favorable conditions, potato plants infected with R. solanacearum may not show
any disease symptoms. In this case, latently infected tubers used for potato seed production may
play a major role in spread of the bacterium from infected potato seed production sites to healthy
potato-growing sites. R. solanacearum can survive for days to years in infected plant material in
soils, infested surface irrigation water, infected weeds, and infected potato washings and sewage.
From these sources of inoculum, bacteria can spread from infested to healthy fields by soil
transfer on machinery, and surface runoff water after irrigation or rainfall. Infected semi-aquatic
weeds may also play a major role in disseminating the pathogen by
releasing bacteria from roots into irrigation water supplies.
Soft rot- Erwinia carotovora subsp caratovora
Symptoms
Infection at two phases are black leg and soft rot. Black lesion appear on the base of the plant
.Systemic and browning of infected tubers. Yellow appearance of the plant. Finally the plants
wilt and die. Lenticels (water soaked brown rot). Rot and collapse of tubers. Soft, reddish or
black ring appear on the infected tuber.
Pathogen
It is a gram negative rod shaped bacterium with 1 to 6 peritrichous flagella.
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Infected tubers attract the flies (Hymelia and Phorlin sp). Spread through immature
contaminated soil and tuber. Optimum temperature 21 to 29 ºC and RH 94%
Management
The pathogen is difficult to control because of long survival both on seed tubers and in soils.
However using disease free seed tubers could minimize the disease incidence. Before planting
the seed tubers are treated with Boric Acid (3% for 30 minutes) and dried in shade. The same
treatment is repeated before the storage of the tubers.
The disease can be reduced by soil application of PCNB (30 kg/ha) at the time of planting.
Following crop rotations with wheat, pea, oats, barley, lupin, soybean, sorghum and bajra checks
the disease development. In plains, treatment of the seed tubers with TBZ + acetic acid + 0.05%
Zinc Sulphate solution or Carbendazim 1% for 15 minutes effectively controls the disease.
Soaking of tubers in Mercuric chloride 0.1% formalin.
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Lecture 12 - Diseases of Cucurbits (2 Lectures)
Cucumber and squash
Vascular Wilt: Erwinia tracheiphila
Symptoms
Symptoms of the disease first appear on a single leaf which suddenly wilts and becomes dull
green. The wilting symptoms spread up and down the runner sometimes as a recurring wilt on
hot, dry days. Soon infected runners and leaves turn brown and die. The bacteria spread through
the xylem vessels of the infected runner to the main stem, then to other runners. Eventually the
entire plant shrivels and dies.
Less susceptible plants, such as certain squash varieties, may show dwarfing of growth
before the wilt symptoms become apparent.
Creamy white bacterial ooze consisting of thousands of microscopic, rod-shaped bacteria
may sometimes be seen in the xylem vascular bundles of an affected stem if it is cut crosswise
near the ground and squeezed. This bacterial ooze will string out forming fine, shiny threads
(like a spider's web) if a knife blade or finger is pressed firmly against the cut surface, then
slowly drawn away about 1 cm.
Two cut stem ends can also be put together, squeezed, then separated to look for shiny
strands of bacteria. The sap of a healthy plant is watery and will not string. Sometimes it helps to
wait several minutes after cutting to perform the test. This technique is useful in field diagnosis
to separate this disease from other vascular wilts. Beware, however, that the technique may not
always work (i.e., no bacterial strings occur yet the plant is still infected). The test works better
73

for cucumbers than for muskmelons. Fruit may also show symptoms. Small water-soaked
patches form on the surface. These patches eventually turn into shiny decayed spots on the fruit.
Pathogen
It is a motile rod with 4 – 8 peritrichous flagella and capsulated. Agar colonies are small,
circular, smooth, glistening white and viscid.
The bacteria apparently overwinter in cucumber beetles and they appear to multiply in
the beetle. The bacterium is not seed borne or soil borne. Bacteria in stems can survive for one
month. Beetles prefer to feed on plants with bacterial symptoms than on healthy plants. Beetle
can remain infective for atleast three weeks. Striped cucumber beetle and the 12- spotted
cucumber beetle help in the spread of the bacterium.
Management
Larger plantings must be protected by insecticides. Some carbaryl (Sevin), malathion, or
rotenone insecticides or combination products are registered to treat cucumber beetles. They will
provide control of the beetles if applied when beetles first appear in the spring. Early control,
beginning as soon as the plants emerge, is most important as a single beetle can introduce the
bacteria. One to four generations of the beetle may occur on unprotected plants and applications
of these insecticides at weekly intervals may become necessary. Apply a light even coating of the
insecticide over the entire plant, especially where the stem emerges from the soil (that is where
the beetles often congregate).
Scab: Cladosporium cucumerinum
Symptoms
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Scab lesions appear on all parts of the vine that are above ground. The first symptoms appear
as light water soaked or pale green spots on the leaves. These spots are numerous and appear on
and between veins. Similar elongated spots develop on petioles and stems. Gradually, the spots
turn grey to white and become angular.
The affected leaves near the tip of the vine may be stippled with dead and yellowish
spots, stunted and crinkled. Fruits are infected at all stages of growth but is most susceptible
while young. Fruit spots are grey, slightly sunken and about 2.0mm in dia.
Pathogen
Conidia are oblong, dark, mostly aseptate.
The fungus probably survives in old cucumber refuse or soil in cracks and on seed. It is
disseminated by insects, clothings and tools.
Disease Cycle
The scab organism survives in soil on squash, melon, and pumpkin vines and reportedly
may grow extensively as a saprophyte. The fungus may also be seed borne. It is disseminated on
clothing and equipment and by insects. The conidia can survive long-distance spread in moist air.
The most favorable weather conditions for disease development are wet weather and
temperatures near or below 21°C. At 17°C the growing tips of young plants are killed. Conidia
germinate and enter susceptible tissue within 9 hr. A spot may appear on leaves within 3 days,
and a new crop of spores is produced by the fourth day.
Management
Crop rotation with corn once in 4 years. Grow resistant varieties like Highmoor and
Maine no.2. Spray Mancozeb 0.2 %.
Musk melon and water melon
Gummy Stem Blight - Mycosphaerella melonis
Symptoms
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Infected stems first appear water-soaked and then become dry, coarse and tan. Older stem
lesions (dead tissue) reveal small black fruiting bodies (pycnidia) within the affected tissues.
Large lesions girdle stems and plants wilt in the heat of the day. Stem lesions on melons exude a
gummy, red-brown substance which may be mistaken for a symptom of Fusarium wilt.
The pathogen can be seed-borne and, thus, can spread by infected seedlings. The
inoculum of the pathogen can also come from other cucurbitaceous host plants and weeds and
infected plant debris in and around the facility. The pathogen produces two types of spores:
asexually-produced pycniospores, and sexually-produced ascospores. Both types of spores are
short-lived once they are released into the environment. However, the pathogen can survive up to
2 years as chlamydospores or mycelium on undecomposed, dry plant debris.
Disease Cycle
The gummy stem blight fungus is both seed- and soil-borne. The pathogen may be
carried in or on infested seed. In the absence of host plants, the fungus can over winter for a year
and a half or more on infected crop residue. The exact length of survival in the Northeast is
currently being studied. The fungus survives as dormant mycelium or as chlamydospores (thick-
walled modifications of the mycelium). In northern areas of the country in the spring, pycnidia
are produced, giving rise to conidia, which serve as the primary inoculum. Conidia are released
through a pore (ostiole) in the pycnidia and if moisture is high, conidia exude as "spore horns"
containing thousands of conidia. Conidia vary in size, are short and cylindrical, with usually one
septum near the middle, or they may be unicellular. Under moist conditions, they are readily
dispersed by splashing water.
Both temperature and moisture are critical for germination, sporulation, penetration of
conidia, and subsequent symptom development, but moisture (relative humidity over 85 percent,
rainfall and duration of leaf wetness from 1 to 10 hours) has the greatest influence. The optimal
temperature for symptom development varies depending on the cucurbit for watermelon 75° F is
optimal, for cucumber 75-77° F, and for muskmelon 65° F. The optimal temperature for
muskmelon reportedly is lower because its resistance increases at high temperatures.
This can be significant to determine when early-season disease scouting should be
initiated for future control. Penetration by conidia is probably direct and does not need to occur
through stomata or wounds. Wounding, striped cucumber beetles, and aphid feeding, along with
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powdery mildew infection, predispose plants to infection. The additional nutrients provided by
such injuries enhance gummy stem blight infection.
Management
Use of disease-free seed and transplants is essential to prevent serious crop losses.
Periodic applications of fungicide like mancozeb @ 0.2% can help limit secondary infections,
especially on fruits. Fall plowing and extended rotations with other crops can significantly
reduce the amount of inoculum in infested fields.
Bacterial Wilt - Erwinia tracheiphila
Symptoms
On cucumber and melon, generally a distinct flagging of lateral and individual leaves occurs.
Affected leaves turn a dull green. Sometimes wilting occurs on leaves that have been injured by
cucumber beetles' feeding, but in many cases obvious feeding is not apparent. Leaves adjacent to
the wilting leaves will also wilt, and eventually the entire lateral is affected. The wilt progresses
as the bacteria move from the point of entry through the vascular system toward the main stem of
the plant.
Eventually the entire plant wilts and dies. If you cut through the stem of an affected plant and
squeeze both cut ends, a white, sticky exudate will often ooze from the water-conducting tissue
of the stem. This exudate is composed of bacterial material that plugs the vascular system of the
plant. Affected stems do not appear significantly discolored. Bacterial wilt is closely associated
with either the striped or the spotted cucumber beetle. The bacteria over winter in the bodies of
adult cucumber beetles. The beetles carry the bacteria when they emerge in the spring.
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The bacteria are spread either through the feces of the beetle or from contaminated
mouthparts. When the beetles feed on young leaves or cotyledons, they open entry points for the
pathogen. Once inside the plant, the bacteria travel quickly through the vascular system, causing
blockages that in turn result in wilting of the leaves. The disease progresses from plant to plant
when a carrier beetle moves through the field or when clean beetles pick up the bacteria from a
diseased plant and fly to healthy plants. Larvae are not known to carry the wilt organism.
Pathogen
It is a motile rod with 4 – 8 peritrichous flagella and capsulated. Agar colonies are small,
circular, smooth, glistening white and viscid.
The bacteria apparently overwinter in cucumber beetles and they appear to multiply in
the beetle. The bacterium is not seed borne or soil borne. Bacteria in stems can survive for one
month. Beetles prefer to feed on plants with bacterial symptoms than on healthy plants. Beetle
can remain infective for atleast three weeks. Striped cucumber beetle and the 12- spotted
cucumber beetle help in the spread of the bacterium.
Management
In general, more bacterial wilt is seen on the edges of fields where beetles first encounter
plants. Larger plantings must be protected by insecticides. Carbaryl, Malathion or rotenone
insecticides or combination products are registered to treat cucumber beetles. They will provide
control of the beetles if applied when beetles first appear in the spring. Early control, beginning
as soon as the plants emerge, is most important as a single beetle can introduce the bacteria. One
to four generations of the beetle may occur on unprotected plants and applications of these
insecticides at weekly intervals may become necessary. Apply a light even coating of the
insecticide over the entire plant, especially where the stem emerges from the soil (where the
beetles often congregate).
Fusarium Wilt - Fusarium oxysporum f. sp. melonis attacks muskmelon and Fusarium
oxysporom f. sp. niveum attacks watermelon.
Symptoms
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Both fungi contribute to damping-off of seedlings, but most significant losses occur after
young plants are infected in the field. Plants infected early in the season often produce no
marketable fruits. Plants that begin to show wilt symptoms at or near maturity produce fewer and
lower quality fruits. The first symptoms of Fusarium wilt are wilting and chlorosis (yellowing) of
older leaves. The wilt is most evident during the heat of the day. Plants may appear to recover by
morning, only to wilt again in the afternoon. Stem cracks and brown streaks often appear near
the crown of the plant and are associated with a red-brown exudate. Fusarium wilt also causes
vascular browning that is visible in stem cross-sections.
The wilt fungus is introduced to new areas on seed. It spreads by wind, equipment and
workers. It can survive long periods in soil as chlamydospores and in association with melon
plant residue.
Management
Planting resistant cultivars is the only reliable way to keep infested fields in production.
Commercially acceptable resistant cultivars exist, but extremely high pathogen populations in the
soil can overcome their resistance. Therefore, methods to reduce Fusarium populations in the
soil also should be employed. These methods include extended rotations with crops other than
cucurbits and fall plowing of severely infested fields.
Anthracnose Colletotrichum orbiculare (= C. lagenarium)
Symptoms
The diagnostic features of anthracnose vary with the host. Sunken, elongated stem
cankers are most prominent on muskmelon, though leaf and fruit lesions also occur. Large
lesions girdle the stems and cause the vines to wilt. Stem cankers are less obvious on cucumbers,
79

but leaf lesions are very distinct. Watermelon foliage affected by anthracnose appears scorched;
sunken fruit lesions are easy to recognize. The anthracnose fungus over winters on diseased crop
residue. There also reported that the pathogen is carried in or on cucurbit seed. In wet conditions
each spring, the fungus releases airborne spores that begin new infections on vines and foliage.
Anthracnose usually becomes established in mid-season, after the crop canopy has fully
developed.
The fungus can infect muskmelon and watermelon in addition to cucumber. The
pathogen survives the winter in infected plant residues. The fungus can also be associated with
seed. As with most fungal diseases, long periods of leaf wetness favor disease development.
Spores are splashed from leaf to leaf, and plant to plant, during irrigation or rain events. Several
disease cycles can occur in a single growing season, resulting in defoliation of severely infected
plants.
Management
Seed treatment with Carbendazim 2g/kg of seed. Spray Mancozeb 2g or Carbendazim
0.5g/lit.
Sudden Wilt
Symptoms
Unlike bacterial wilt, which can occur any time during the season, sudden wilt generally
occurs late in the season and is closely associated with a heavy fruit load on the plant.
Cucumbers and melons appear to be most sensitive to sudden wilt. Initial symptoms are a slight
flagging of the plants in midday even when abundant moisture is present. This flagging will
continue to worsen so that, by the third or fourth day, many of the plants are completely wilted.
Disease progression is rapid, hence the name sudden wilt. After five to six days, all of the vines
have melted down and only the immature fruits are left in the fields. Affected plants appear to
lack feeder roots; other roots become slightly misshapen and thick. Currently it is thought that
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